1. Field of Invention
This invention relates to expansion heat engines, both internal and external combustion, specifically to allow such engines to operate in an enclosed environment where ambient air is not available or where the exhaust gases and combustion byproducts must be contained. Example of such environments are: submarines and autonomous underwater vehicles; underwater and subterranean power generating systems; in space or at very high altitudes.
In a conventional air-aspirated internal combustion engine air, ingested on the intake stroke, is composed of Nitrogen (N.sub.2), Oxygen (O.sub.2) and water vapor (H.sub.2 O). This gas is mixed with fuel and ignited in combustion to reduce the fuel and O.sub.2 to CO.sub.2 and H.sub.2 O and produce sensible heat. This mixture of N.sub.2, CO.sub.2 and H.sub.2 O vapor becomes the "working gas" and ultimately the exhaust. The heat of combustion raises the temperature and pressure of this working gas, which can be mechanically harnessed to do work. Of the working gas in an air-aspirated engine (N.sub.2, CO.sub.2, H.sub.2 O, residual O.sub.2 and trace gasses) N.sub.2 is the principal working gas component. It is possible to separate the N.sub.2 from the combustion byproducts in the exhaust, (CO.sub.2 and H.sub.2 O) and recirculate this "reconditioned" N.sub.2 in a closed loop or cycle by replenishing the O.sub.2 and introducing fuel as required to meet engine power requirements. The molecular mass, equivalent specific heat and gamma value of the initial gas charge ingested by the engine must be replicated on each intake stroke if engine performance is to be maintained as designed. The excess CO.sub.2 and H.sub.2 O in the exhaust must be removed or "scrubbed" from the exhaust in order for the N.sub.2 to be recycled as the principal working gas. It is the complexity, inefficiency and cost of separating and removing the byproduct CO.sub.2 from the N.sub.2 exhaust that has been the limiting complication in Prior Art attempts to produce a workable closed cycle engine system.
It is also desirable to adapt conventional, air-aspirated engines for this application. The significant costs associated with the design, development and production, of a highly engineered product have been amortized by the engine builder making the unit cost affordable. Also, there exists a broad spectrum of commercial engines available to choose from that can be adapted for closed cycle operation using this invention. The best engine can therefore be matched to the job. An example of such an engine is the conventional diesel, either 4-stroke cycle or 2-stroke cycle that is widely used in marine, transportation and stationary power applications. However, this invention is applicable to Otto, Brayton and Sterling cycle engines equally as well.
The typical diesel 4-stroke cycle begins with the intake stroke ingesting air from the atmosphere, which is approximately 79% nitrogen and 21% oxygen. The following compression stroke raises the temperature of this gas to ignition temperature; fuel is injected and the subsequent combustion process consumes the fuel, all or part of the oxygen and the sensible heat released raises the temperature of the product gases (Principally N.sub.2 with lesser amounts of CO.sub.2 and H.sub.2 O). At maximum theoretical efficiency, a stoichiometric ratio of fuel and O.sub.2 exists and only CO.sub.2 and H.sub.2 O will result from combustion; however, the exact ratio of oxygen and fuel required for complete combustion seldom exists, and small amounts of unused O.sub.2 and Carbon Monoxide (CO) are by present in the working gas exhaust, which is principally N.sub.2. This high-pressure gas forces the piston down on the power stroke. At the bottom of piston travel the exhaust valve opens; the subsequent exhaust stroke purges the cylinder and the cycle repeats starting with the intake stroke. The high pressure of this mixed gas resulting from combustion in a confined space, the engine combustion chamber, accomplishes work on the subsequent power stroke by moving a piston-crank assemble, by rotating a turbine wheel or causing other mechanical or electrical apparatus to function. The engine typically drives a pump, electrical generator or mechanical transmission to accomplish useful work.
In an engine operating in an open environment new air is ingested and the exhaust is vented to the atmosphere at each cycle. The earth's atmosphere is essentially an infinite source of O.sub.2 and an infinite sink or buffer for the exhaust. However, in a closed system the buffer volume is severely restricted and exhaust gas must be retained, processed and recirculated under exacting control as part of the engine operating process. O.sub.2 must be replenished from secondary storage. The gamma factor of the gas ingested on each intake stroke must be maintained essentially constant by removing excess combustion byproducts from the exhaust. The gamma factor is the ratio of specific heat at constant volume over the specific heat at constant pressure and is succinct to a given gas or mixture of gasses. The inert gas, N.sub.2, that is the principal component in the exhaust gas, must be reconditioned to establish the required gamma value by removing the combustion byproducts, CO.sub.2 and H.sub.2 O. It then can be recirculated. Oxygen and fuel are added as necessary.
2. Description of Prior Art
Most commercial engines are designed for N.sub.2 to be the principal component of the working gas. If the quantity of CO.sub.2 or H.sub.2 O in the recirculated gas is allow to build up by not effectively removing the excess, the gamma value will change which will adversely alter combustion temperature and pressure. This can cause damage to the engine or prevent the engine from functioning as intended. Precise control of the gamma value and mass-ratio of inert gas, oxidizer, water vapor and fuel is essential for an engine to function as it has been designed. The major difficulty involved in closed cycle system has been in separating the CO.sub.2 from the working inert gas. Another, third, inert gas has been used as a diluent in this process to correct the gamma value of the mix. Some Prior Art processes use Argon, Neon or other inert gas as a diluent, however, separating the CO.sub.2 from two mixed inert working gasses further complicate the exhaust reconditioning process.
Prior Art:
Closed Cycle Rankine Cycle Steam Engine; U.S. Pat. No. 4,698,974; to the Garrett Corporation, Oct. 13, 1987, describes a steam turbine propulsion system enclosed within a pressure vessel. In its intended use Hydrogen (H.sub.2) and Oxygen (O.sub.2) are combined to produce superheated steam as the combustion byproducts. H.sub.2 is formed by reaching water with a solid metal fuel and O.sub.2 is delivered from high-pressure tank storage inside the pressure vessel. The only apparent similarity is that this steam turbine system uses a pressure vessel.
Prior Art:
Apparatus and Method for Energy Conversion Using Gas Hydrates; U.S. Pat. No. 5,613,362; to Billy D. Dixon, Mar. 25, 1997, describes a system enclosed in two (2) separate pressure vessels that uses the nearly isothermal compression of the gases associated with hydrates to produce energy and a differential gas pressure capable of doing work. The only apparent similarity is the use of pressure vessels as containments.
Prior Art:
Closed Cycle Rankine Cycle Steam Engine; U.S. Pat. No. 4,698,974; to the Garrett Corporation, Oct. 13, 1987, describes a steam turbine propulsion system enclosed within a pressure vessel. In its intended use Hydrogen (H.sub.2) and Oxygen (O.sub.2) are combined to produce superheated steam as the combustion byproducts. H.sub.2 is formed by reaching water with a solid metal fuel and O.sub.2 is delivered from high-pressure tank storage inside the pressure vessel. The only apparent similarity is that this steam turbine system uses a pressure vessel.
Prior Art:
Closed Cycle Engine; U.S. Pat. No. 4,674,463; to Cosworth Engineering LTD, Jun. 23, 1987, has attempted to control the quality of recirculated gas by removing some of the excess exhaust byproducts by solvent absorption. A second inert, or diluent gas is introduced, Argon (Ar), in a complicated approach to preserve the gamma value of the recirculated working gas. Excess H.sub.2 O is cooled, condensed and removed by conventional processes.
Prior Art:
Closed Cycle Power System Process; U.S. Pat. No. 3,658,043; to Aerojet-General Corporation, Aug. 20, 1969, excess CO.sub.2 is removed by chemical conversion using alkaline metals and caustic solutions. Hydrogen (H.sub.2) and water vapor are added in an attempt to preserve the gamma value of the ingested gas.
Prior Art:
Closed Cycle Power System; U.S. Pat. No. 5,016,599; to Cosworth Deep Sea Systems LTD, May 30, 1990, attempted to remove excess CO.sub.2 by compressing the mixed exhaust gas and injecting it into water where it is dissolved into solution. The pressure of this solution is subsequently reduced allowing much of the inert gas to flash quickly out of solution leaving some of the carbon dioxide in solution as carbonated water; which is then disposed of by pumping it overboard. Some of the inert gas is lost in this effluent as well. Both factors make regulation of the gamma value of the recirculated gas difficult to control, particularly if the load on the engine is variable. This system however, is not a true closed system, as effluent water must be discharged overboard.
Prior Art:
Closed Cycle Power System; U.S. Pat. No. 5,177,952; to Rockwell International Corporation, Jan. 12, 1991, uses alkaline metal superoxide to react with water, produce hydrogen (H.sub.2) gas and metal hydroxide. The hydroxide then reacts with and removes some of excess carbon dioxide. The H.sub.2 gas produced is used as fuel in this process. Water vapor becomes the principal working gas. This system is also complex, difficult to control and costly to sustain because the chemicals are expensive and dangerous to handle.
The various closed cycle engine systems heretofore have used complex processes, both mechanical and chemical, to deal with the CO.sub.2 byproducts which must be removed form the exhaust in order to retain the gamma value of the ingested gas and therefore be able to use a commercial internal combustion engine for the proposed closed cycle power generating system. These systems have known disadvantages:
A. The commercial engines available presume a gamma value of ingested gas to be that of a 79/21% ratio of N.sub.2 and O.sub.2 ; or that of standard air. This value is difficult to maintain when the combustion byproduct, CO.sub.2, is mixed with the working gas, N.sub.2, and must be removed or separated. PA0 B. The design assumes the absolute pressure of ingested air will be at or near atmospheric pressure (14.7 psia, 1080 bar) PA0 C. That the combustion byproducts, CO.sub.2 and H.sub.2 O, must be removed from the N.sub.2 in the exhaust in order for the recirculated gas to function in the engine. PA0 D. That hazardous, expensive chemical reactants or solvent absorption are the methods of choice for removing excess CO.sub.2. PA0 E. These engines do not respond quickly to variable engine loads.